Drilling Bit PDF

10-08-2024 DRILLING BIT M.Sc in Applied Geology...

10-08-2024 DRILLING BIT M.Sc in Applied Geology Dr Himangshu Kakati IIPE Visakhapatnam Rotary Drilling Bit Roller Cone Bit Heart of the drill string Polycrystalline Diamond Bit (PDC) Drill bit crushes the rock under the combined Diamond & Thermally Stable PDC (TSP) Bit action of weight on bit and rotary speed. Chippings are flushed away by the circulating fluid, to allow the bit to attack a new surface of rock. 1  10-08-2024 Roller cone bit employs cones which rotate about their own axis or about the bit axis. Milled teeth bit: Bit cones have milled teeth cut from the body of the cone. Suitable for soft formations, Inserted Teeth bit: Tungsten carbide buttons inserted into the cones. This type bits can drill medium to hard formations. Roller Cone Bit Milled teeth Roller Cone Bit Inserted teeth Roller Cone Bit Three-cone bit consists of three equal-sized cones and three identical 'legs'. Each cone is mounted on bearings Roller Cone Bit which run on a pin that forms an integral part of the bit leg. The three legs are welded together and form the cylindrical section, which is threaded to make a pin connection to provide a means of attachment to the drill string. 2  10-08-2024 Each leg is provided with an opening for fluid circulation, the size of which can be reduced by fitting nozzles of different sizes. Nozzles are used to provide constriction in order to obtain high jetting velocity for efficient hole cleaning. Mud pumped through the drill string passes through the pin bore and through the three nozzles, with each nozzle Roller Cone Bit accommodating one-third of the flow, if all the nozzles are of the same size. (a) Journal angle; (b) Amount of offset; (c) Teeth; (d) Bearings Roller Cone Bit: Design Factor Journal Angle: The journal angle is defined as the angle formed by a line perpendicular to the axis of the journal and the axis of the bit. Journal angle directly affects the size of the cone. An increase in journal angle will result in a decrease in the basic angle of the cone and, in turn, cone size. The smaller the journal angle the greater the gouging and scraping action by the three cones 3  10-08-2024 Roller Cone Bit: Design Factor As the journal angle increases from zero, the cutters must be shaped (by removal of excess steel, as to prevent the three cones interfering with one another. Smaller Journal angle, greater WOB Influence of journal angle on cone size: (a) 0° (b) 15° (c) 30° (d) 36° (e) 45° Optimum journal angles for soft: 33° & hard roller: 36° Cone offset: defined as the horizontal distance between the axis of the bit and a vertical plane through the axis of the journal. Tri-cone roller Bit under load has two motion Roller Cone Bit: Design Factor (i) Axial motion about its journal axis (ii) Circular motion about the bit axis. Due to the presence of two types of motion, it possesses a slipping tendency over the formation which will provide the gouging action to the bit. The teeth attached to the cone will be subjected to moment and will provide a twisting action. More the offsetting of the bit, more will be its twisting action to the formation. 4  10-08-2024 Offsetting and formation characteristics Soft Formation: Twisting action provided by bit will be very much effective. By virtue of formation's low compressive strength the bit tooth will have less resistance to penetration into the Roller Cone Bit: Design Factor formation. This will ensure easy insertion of the tooth. After insertion, when the bit tooth provides a twisting action, it easily shears off the formation. This is important in the sense that energy required in shear failure of the rock is less than that required for compressive failure. As the rock does not have much over all resistance, formation can not abrade the tooth face very quickly. Hard Formation: High degree of resistance against its failure. So, if the cone is off-setted and tooth is allowed to twist against the formation, it abrades away the tooth face. So, while designing a bit for the hard formation, care is taken that its offset angle is low or even to the degree of zero. Cone Profile Rolling action of bit is dependent on cone profile. Soft formation bit cones deviate substantially from true rolling because, they have Roller Cone Bit: Design Factor two or more basic cone angles, none of which has its apex at the center of bit rotation. Produce gouging action. Cone angles are such that their apex lies close to the bit center. Since slippage is controlled by center, bits produce chipping-crushing action. 5  10-08-2024 Tooth Drill bit have (a) slender and long teeth or (b) short and stubby teeth Long teeth and widely spaced : For soft low compressive strength rock Roller Cone Bit: Design Factor and easily penetrated. Penetration is achieved by WOB. Rotation helps in removing broken chips. Long teeth and widely spaced : For soft low compressive strength rock and easily penetrated. Penetration is achieved by WOB. Rotation helps in removing broken chips. Short teeth and closely spaced: For hard formation. Hard formation are difficult to penetrate. Short teeth are less likely to be broken. Teeth apply load over a much larger area and break the rock by a combination of crushing, creation of fracture and chipping. Teethe are not intended to penetrate but simply to fracture it by applying compressive load. Types of Tooth Milled Type: Milled teeth are cut from the cone body. One side of the tooth being hard-faced with a resistant material such as tungsten carbide to provide a self- Roller Cone Bit: Design Factor sharpening effect. As the unfaced side of the tooth wears away, it leaves a sharp edge suitable for efficient drilling. Suitable for drilling very soft to soft formations in which moderate weights are required to fracture the rock. Inserted Type: Inserts (or buttons) are made of tungsten carbide and are cold-pressed into holes already drilled in the cone shell. Chisel-shaped inserts are used to drill soft rocks, while round or hemispherical inserts are used to drill medium to hard rocks. 6  Roller Cone Bit: Design Factor Roller Cone Bit: Design Factor Types of Tooth 10-08-2024 7  10-08-2024 Bearing Bit bearings are used to perform the following functions: (a) support radial loads; (b) support thrust or axial loads. Roller Cone Bit: Design Factor Currently, two different bearing arrangements are in use: (1) anti-friction bearings; and (2) friction bearings. Anti-friction bearings: (1) roller-ball-roller bearings; and (2) roller-ball friction bearings. Roller-ball-roller bearings Roller ball friction bearing Roller Cone Bit: Design Factor Journal (friction) Bearing Allows high WOB to be used because the load is transmitted readily over a large surface area. Coating a metal alloy inlay which reduced the friction coefficient. A thin film of clean lubricant is essential to keep bearing surface out of contact. 8  10-08-2024 Polycrystalline diamond compact bit is a new generation of the old drag Polycrystalline Diamond Compact (PDC) bits or fishtail bit. Employs no moving parts. Break the rock in shear and not in compression, as is the case with roller cone bits, or by a ploughing/grinding action, as is the case with diamond bits. PDC bits are also known as 'stratapax' bits. PDC bit fails the rock in shear limits its application to the drilling of rocks of soft and medium hardness. Breakage of rock in shear requires significantly less energy than in compression. Thus, less weight on bit can be used, resulting in less wear and tear on the rig and drill string. Polycrystalline Diamond Compact (PDC) bits 9  10-08-2024 Drill blank: Cutting element in PDC bit Polycrystalline Diamond Compact (PDC) bits Polycrystalline Diamond also known as PCD is produced synthetically by sintering together many (Poly) diamond particles, usually in the size of 2 to 30 microns of a meter, with a metal binder at high temperature and high pressure. The PCD material may contain 90-95% diamond particles and the rest is the binder. The drill blank is made by bonding a layer of polycrystalline man-made diamond to a cemented tungsten carbide substrate in a high-pressure, high-temperature process to produce an integral blank. Blank having the hardness and wear resistance of diamond complemented by the impact resistance of the cemented tungsten carbide layer. During drilling the compact provides a continuous sharp cutting edge, owing to continuous microchipping of the diamond surface resulting from wear, necessary for rock cutting. Polycrystalline Diamond Compact (PDC) bits 10  10-08-2024 Bit body material: heat-treated alloy steel and PDC bit design is influenced by nine variables: Polycrystalline Diamond Compact (PDC) bits (2) a tungsten carbide matrix (1) bit body material; Bit Profile: affects cleaning and stability of the (2) bit profile; hole and gauge protection. (3) gauge protection; Design Factor (4) cutter shape; (5) number or concentration of cutters; (6) locations of cutters; (7) cutter exposure; (8) cutter orientation; and (9) hydraulics Gauge protection: provided by tungsten carbide inserts placed near the edges, while the matrix body bit Polycrystalline Diamond Compact (PDC) bits utilises natural diamonds for gauge protection. Cutter Shape: (1) standard cylindrical shape; (2) the chisel (or parabolic) shape; and (3) the convex shape. Design Factor Concentration of cutters: Longer bit life is generally obtained with greater concentration of cutters. However, the penetration rate decreases with increasing concentration, owing to the difficulty of cleaning the areas between the cutters. Extreme right: With more blades, small and numerous cutter suitable for hard formation 11  10-08-2024 Location of cutters: Field experience and fracture mechanics models are used to locate cutters for Polycrystalline Diamond Compact (PDC) bits maximum cutting and minimum wear and torque. Cutter exposure: Penetration rate increases with increased cutter exposure; however, greater exposure makes the cutter more vulnerable to breakage. Design Factor Cutter orientation: is described by back and side rake angles. As the rake angle increases, the penetration rate decreases The cutting elements of a diamond bit consist of a large number of small-sized diamonds geometrically distributed across a tungsten carbide body. Diamond bits No moving parts Normally used for hard and abrasive rock drilling and when longer bit runs are required in order to reduce trip time, e.g. in deep wells, and in offshore drilling, where rig costs are very high. Large diamonds are used to drill soft rocks, since these rocks can be easily penetrated. For hard rocks, small-sized diamonds are used, since the diamonds cannot penetrate very far in such rock. Thermal conductivity of diamond is he highest of any mineral, thus diamond dissipate heat from its cutting structures very quickly. Thus protect diamond loss by burning or thermal fracture. 12  10-08-2024 Bit 13